The present invention deals with mirrors. More particularly, the present invention deals with a vision enhancement device in the form of a computer generated virtual replica of a mirror.
Mirrors associated with motor vehicles assist the driver by providing spatial awareness of traffic conditions behind (and to the sides of) the drivers vantage point. Conventional mirrors have several disadvantages. A first of these disadvantages is the blind zones associated with a conventional mirror. Mirrors of conventional widths, on automobiles, provide a viewing angle from approximately 15 degrees to 30 degrees. Typically, drivers set the mirrors such that there is a great degree of overlap in these already narrow fields of view. Obstructions and limitations to the fields of view are due to the location and size of real mirrors. The problems associated with large blind spots, or blind zones, are aggravated for elderly people who may have less acute peripheral vision and/or may encounter difficulty in turning their head.
Another problem with conventional mirrors is that the view from the mirror to the rear or side of the vehicle is often obstructed. For example, a passenger's head or vehicle pillars may obstruct the rearward or sideward looking views from the driver or from the mirror. Similarly, on large vehicles, such as trucks and sport utility vehicles, the views from the mirrors can be obstructed by portions of the vehicle body itself.
Another disadvantage presented by conventional mirrors is vibration. While this disadvantage is not as pronounced on small passenger cars, it presents a great deal of difficulty on large, commercial vehicles. As such a vehicle encounters uneven road surfaces, induced torques are transmitted to the mirror mounting hardware which causes the mirror to vibrate. These vibrations can be at frequencies which significantly disrupt the ability of the driver to distinguish meaningful information from the mirror.
Also, because the shaky reflection from a vibrating mirror is caused by the changing mirror orientation mirror angle, a change of θ in mirror orientation creates a change of 2θ in image position. Therefore, as the mirror oscillates back and forth, the image also oscillates back and forth with twice the magnitude of the mirror oscillation, leading to a blurred image.
Another disadvantage of conventional mirrors is that they must be quite large in order to provide a significant rearward or sideward looking view. However, any mirror mounted forward of the operator obstructs the forward view. Therefore, large conventional mirrors can undesirably obstruct the operator's forward looking view.
Another disadvantage arises from the fact that many commercial vehicles use convex mirrors, in addition to flat mirrors. The convex mirrors show a wider area than flat mirrors. However, objects reflected in convex mirrors appear smaller than when looking at the same objects in a flat mirror. Due to this effect, the object appears to be further away from the host vehicle than it actually is. This requires drivers to allow for distance overestimation when maneuvering the vehicle.
One prior art technique for addressing some of the deficiencies of conventional mirrors involves the use of periscopes. Such a periscope consists of the usual inside mirror coupled to an ensemble of mirrors located on the roof of the vehicle. These mirrors are presumed to have an unrestricted field of view. However, such periscopes have been found to be very large and bulky, and adversely increase the air resistance and drag of the vehicle.
Other prior art approaches to addressing the problems associated with conventional mirrors involve a TV camera, fitted with wide angle optics installed on the rear of the vehicle. This technique also required a monitor in the instrument panel of the vehicle to provide a wide, unobstructed image. Such a setup requires a one meter wide display to cover a space at a distance of 70 meters away from the camera, at a one-to-one magnification. This translates to approximately a 90 degree field of view. In addition, such a TV monitor hooked up to a rearward looking camera does not operate satisfactorily under poor visibility conditions. The display can also lead to confusion because of the likely absence of the right-left lateral inversion associated with a reflected image.